Degenerative spinal stenosis is a common cause of back and leg pain. A typical causative factor of spinal stenosis is a thickening of bone and/or ligaments into the spinal nerve channel, which thickening applies pressure to the nerves passing through the spinal column.
FIGS. 1A and 1B illustrate a vertebra 100 in top and side views respectively, illustrating common types of spinal stenosis. A vertebra 100 comprises a body 102 and processes 103, which surround laminas 108 and pedicles 111. The laminas and the pedicles define a spinal channel 106, in which a spinal cord 104 is disposed. A ligament (yellow ligament, ligamentum flavum) 110 separates spinal cord 104 from the lamina 108.
FIG. 1B shows a side view illustrating a pair of inferior articular processes 112.
Typical causes of spinal stenosis include:
(a) thickening and calcification of ligament 110;
(b) thickening of lamina 108; and
(c) hypertrophy of the joint between two vertebra and especially the inferior articular processes 112, for example due to degenerative changes.
Most often, spinal stenosis is caused by a combination of (a) and (c) above.
One known surgical procedure for treating spinal stenosis is lumbar laminectomy in which the bony outer layer of the spinal column is removed, to allow room for cord 104. In a variation of this procedure, windowed laminectomy, only plugs of the bone are removed, for example at articular processes 112, thereby reducing trauma to the spine and associated tissues.
One problem with the full laminectomy methods is that the spine loses stability so the spine usually needs to be fused. Another problem is that laminectomy is a major surgery, often not suitable for the elderly, who, as a group, are more likely to suffer from spinal stenosis than other age groups. In addition, laminectomy has an associated overall surgical mortality rate of about a 1%.
German patent publication DE 40 36 804 A1, the disclosure of which is incorporated herein by reference describes a device for removing portions of the spine, apparently for correcting spinal stenosis, for example stenosis caused by spondylolytic damage.